1. Field of the Invention
The present invention relates to a wavelength tunable surface emitting laser and an optical coherence tomography apparatus using the same.
2. Description of the Related Art
A wavelength tunable laser capable of changing a laser oscillation wavelength can be expected to be applied to various fields including communication, sensing, and imaging, and thus, is vigorously researched and developed in recent years.
As a kind of such a wavelength tunable laser, a structure is known that is so-called a MEMS-VCSEL in which a laser oscillation wavelength of a vertical cavity surface emitting laser (VCSEL) is controlled through a micro electro mechanical systems (MEMS) technology.
A VCSEL is generally formed by sandwiching an active layer between a pair of reflectors such as distribution Bragg reflectors (DBRs), and a laser is oscillated at a wavelength in accordance with a cavity length determined by an optical path length between the reflectors. In a MEMS-VCSEL, by mechanically moving a location of one of the reflectors, the cavity length can be changed to change the laser oscillation wavelength (see, for example, U.S. Pat. No. 6,549,687).
In a MEMS-VCSEL, an amount of change in laser oscillation wavelength with respect to an amount of change in reflector location is sometimes referred to as a wavelength tuning efficiency. It is known that the magnitude of the wavelength tuning efficiency is affected by the cavity length and a kind of surface coating (“Broadband MEMS-Tunable High-Index-Contrast Subwavelength Grating Long-Wavelength VCSEL”, Il-Sug Chung et al., IEEE Journal of Quantum Electronics, Vol. 46, NO. 9, p. 1245-1253, 2010).